The 20-month conflict in Syria has reached “new and appalling heights of brutality and violence” as the government steps up its shelling and air strikes and rebels boost their attacks, U.N. Secretary-General Ban Ki-moon said on Friday.

Ban and international Syria mediator Lakhdar Brahimi addressed the 193-member U.N. General Assembly on the revolt against Syrian President Bashir al-Assad, which began as peaceful rallies calling for democracy but grew to an armed struggle after the military cracked down on protesters.

The fighting has killed about 40,000 people, making it the bloodiest of Arab uprisings that have ousted entrenched leaders in Tunisia, Egypt, Libya and Yemen since early last year.

“The government has intensified its campaigns to root out opposition strongholds and has increased shelling and air strikes,” Ban said. “Opposition elements also have stepped up their attacks. I am horrified and saddened and condemn the seemingly daily massacres of civilians.”

Syrian air force jets bombarded rebel targets on Friday close to the Damascus airport road and a regional airline said the violence had halted international flights. The Internet and most telephone lines also were down for a second day in the worst communications outage of the conflict.

Ban said with the onset of winter, up to 4 million people in Syria would be in need and that he expected to number of refugees – currently about 480,000 – to hit 700,000 by early next year. He appealed for more humanitarian aid and said he would soon visit refugee camps in Jordan and Turkey to assess the situation.

Brahimi said rebel forces had made gains on the ground in the past few weeks, but the government remained confident that it has the upper hand.

“The areas of territory that they (the rebels) control are expanding, and with strategic value in some cases,” Brahimi said. “In Syria itself, there is no trust between the parties. They do not even define the problem in the same terms.”

Brahimi told the General Assembly that Syria was in danger of becoming a failed state and stepped up his pressure on the Security Council, which is deadlocked over taking stronger action on Assad, to adopt a resolution backing his peace bid.

The United States and European council members blame Russia, a staunch ally and key arms supplier for Assad’s government, and China for the council’s inaction on the conflict. Moscow and Beijing have vetoed three resolutions condemning Assad and reject the idea of sanctions. Diplomats say nothing has changed.

“Any peace process must include … a binding agreement on the cessation of all forms of violence,” Brahimi said.

“For the fighting to stop, a strong, well planned observation system must be put in place,” he said. “Such observation can best be organized through a large, robust peacekeeping force – and, naturally, that cannot be envisaged without a Security Council resolution.”

If there were a more sustained ceasefire, the U.N. Department of Peacekeeping Operations has told Brahimi it could put together a force of up to 3,000 monitors to keep fighters separated and maintain the truce, diplomats say.

“Difficult as it has been for the council to reach a consensus on an implementable roadmap for Syria, I nevertheless feel that it is here, and only here, that a credible, implementable process can be put together,” Brahimi said.